Hello everyone. I have designed a dual-band patch antenna. The antenna gives good gain at both the resonating frequencies. but here is the problem that I get a dip on the broadside in the antenna radiation pattern on one frequency but still this frequency shows high directivity. can this be possible? Please comment
Yes, there maybe a problem at the symmetry. This means, at that frequency, it is providing null at that direction at the front side. It should not be happened. The both e-plane and h-plane should be symmetrical
Dear Sapna Chaudhary ,
Clearly there is a null in the broadside direction. That means that in that band the currents are opposite and therefore the null appears. I understand that it is not a single patch but two patches? I should see the figure to explain better but clearly right now you don't have an antenna that works in two bands, at least as far as the radiation pattern is concerned.
Thank you Atik Mahabub and Miguel Ferrando-Rocher for the reply. Miguel Ferrando-Rocher it is not an array it is single patch.My main concern is that how is it possible that this band have high directivity.
Your single patch is probably one-wave resonant, rather than half-wave resonant, at the higher frequency. This means that opposite ends of the patch are radiating out of phase instead of in-phase. This results in cancellation at broadside, where both ends are the same distance, but in a lobe in each of the directions where there is an extra-half-wavelength path difference in the distances to the two ends of the patch.
Dear Sapna,
understood. In that case clearly what prof. White is pointing out to you is happening.
A possible solution would be to introduce some additional degree of freedom in the patch to achieve the dual-band behavior you desire.
Best regards,
If your patch is resonant at one wavelength then it will be about 0.81 wavelengths long, based on the lobe angle.
Thank you Malcolm White for the explanation. I understand the concept of dip at this frequency but what can be the possible reason for its high directivity. that is my confusion.
It has narrower lobes than at the lower frequency because the antenna is now wider in wavelengths than at the lower frequency. The projected aperture width for each lobe is about 0.81 cos(38 degrees) wavelengths.
Thanks Malcolm White . but could you please elaborate in detail the line "The projected aperture width for each lobe is about 0.81 cos(38 degrees) wavelengths"
The lobes are roughly 38 degrees from normal. At this angle one end of the patch has to be one half wavelength further away than the other end to compensate for them being 180 degrees out of phase. This means the separation is half a wavelength divided by sin 38 degrees, which is about 0.81 wavelengths.
When seen from the direction of the lobe, i.e. 38 degrees from normal, this separation looks like 0.81 cos 38 degrees. Look up projected aperture. Look up the relation between aperture and beamwidth. Look up the relation between phase difference between radiators and the beam angle.
- Badges
- Science topic